This invention relates to centrifuges, and is particularly applicable to analytical centrifuges, i.e. centrifuges having an optical or other radiation system for sensing the radiation absorption properties of material whilst it is being centrifuged.
Modern centrifuges have the requirement that they should be operable with a variety of rotors of different types and ratings. Each rotor has its own maximum permissible speed rating to avoid overspeed and damage to the rotor. In the past, mechanical systems have been employed to sense the speed rating and effect some corresponding limitation upon a motor speed control circuit whereby an operator will be overriden should he select too high a speed. In more modern systems a more direct method is employed wherein maximum permissible speed of the rotor is directly sensed, when it occurs. In practice, each rotor is provided with a plurality of distinct portions directly related in number with the maximum permissible speed. These portions are sensed optically or magnetically to create an electrical signal with a frequency proportional to actual rotor speed and to the speed rating. This signal is compared with a fixed frequency, and when equality is sensed, it is known that the rotor has reached its speed rating. However, this system operates in steps, i.e., with a given fixed frequency, there are only certain speed ratings which can be sensed. The sizes of these steps are significant in modern high speed centrifuges, where each rotor can accommodate only a limited number of portions, e.g. 5 to 15.
It is an object of the present invention to provide the possibility of a continuous range of speed ratings.